[wasm][eh] Add WebAssembly.Tag.toStringTag()

R=jkummerow@chromium.org

Bug: v8:11992
Change-Id: I4229a6fff8d956a5baa9ab9d5028f9abc20d4039
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3071405


Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76109}